Process for the beneficiation of sylvinite ore



3,052,349 Patented Sept. 4, 1962 3,052,349 PROCESS FOR THE BENEFICIATION F SYLVINITE ORE Robert E. Snow, Lakeland, Fla., assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Filed Aug. 29, 1960, Ser. No. 52,360 16 Claims. (Cl. 2099) The present invention generally relates to the beneficiation of potash ores. More particularly, it relates to a combination process whereby high K 0 content concentrates may be obtained from sylvite ores. Still more particularly, it relates to a process utilizing a combination of electrostatic separation and magnetic separation steps wherein concentrated sylvite values are obtained from ores of the sylvinite type.

Potassium-containing minerals, such as sylvinite and langbeinite, vare found in the earths crust in substantial quantities. Sylvinite, a naturally occurring mineral principally comprising sylvite and halite, is mined in large quantities in New Mexico and elsewhere in the United States, Canada and Europe. Since both sylvite and halite are water-soluble, the separation of the valuable potassium chloride by flotation procedures has presented many problems and, despite widespread use, represents a. basically undesirable beneficiation process. Langbeinite, a potassium sulfate-magnesium sulfate complex, has presented similar beneficiation problems, as have other potash ores containing water soluble potassium values.

Separation of various materials including ores by electrostatic procedures long has been viewed by the art as a desirable expedient both from the standpoint of efficiency and economy. In practice, some success has been achieved in separating mixtures of conductive materials and mixtures of conductive and nonconductive materials. Electrostatic separation processes have also been developed for effecting separations between essentially nonconductive materials and especially nonconductive materials such as the naturally occurring mixtures of sylvite and associated gangue substances. However, when a potash ore contains a relatively large amount of waterinsoluble components or slimes, considerable difficulty has been experienced in effecting the desired beneficiation in electrostatic processes, and the process of this invention effectively beneficiates such ores.

In successful prior art conductivity-type electrostatic separations, advantage has been taken of the differential ability of various conductive materials to dissipate an electrical charge. In the usual conductivity separations of the prior art, the dry, comminuted mixture is fed to the grounded conveyor roll of a roll-type electrostatic separator, and in the course of delivery to the electrostatic field created by a closely spaced, oppositely charged electrode, is charged by bombardment with electrons, usually in the form of corona discharge. The conductive or more conductive components of the mixture rapidly lose their charge to the conveyor roll and either follow their natural trajectory into the collection zone below or else are horizontally displaced by the attractive and repulsive forces of the electrostatic field. 'Ihe nonconductive or less conductive components retain their charge longer than the conductors, are attracted by the conveyor roll in varying degree, and either fall from or are scraped from the surface of the conveyor roll at points circumferentially beyond the normal point of gravitational dissociation.

It at once will be recognized that mixtures of essentially nonconductors do not readily lend themselves to separation by the conductivity method described. The art, therefore, has been forced to various expedients in an eflort effect commercially attractive separations.

It also has been discovered that under certain conditions, particulate nonconductive materials will assume an electric charge by contact electrification. Such charge may be developed by contact with metal, a grounded conductor, or by particle-to-particle content. The charge developed by an isolated, pure material in contact with a metal or grounded conductor, however, aiiords no basis for accurate prediction of the type or magnitude of charge which the same particle will assume when contacted with a dissimilar nonconductive particle during intentional agitation or as a result of normal manipulation. When, for example, feldspar and quartz are individually contacted with a metal such as iron, aluminum, or zinc, the feldspar assumes a weakly negative charge while quartz becomes strongly negatively charged. When a comminuted feldspathic ore containing feldspar and quartz is charged by particle-to-particle contact, quartz becomes negatively charged and feldspar assumes a positive charge.

The mere fact that nonconductive mineral substances will assume differential charges regretably does not permit ready electrostatic separation. Instead, the charge differential must be of sufiicient magnitude so that an electrostatic field of practical strength will efiect the degree of horizontal particle displacement requisite to commercial operations. Accordingly, the art is confronted with the problem of ascertaining conditions under which the required charge differential may be achieved with the recognition that the charging characteristics of any given mineral component in a particular association are unpredictable.

It previously has been determined that an acceptable separation of sylvite from halite may be achieved by heating liberated potash ore to a temperature above F. but below the melting point of the ore, differentially charging the heated ore by contact electrification, and then passing the diiierentially charged ore through an electrostatic field to produce a concentrate of increased K 0 content.

The art has also developed an electrostatic method of beneficiating potassium salt-containing materials which includes the step of treating a substantially dry mixture of the potassium salt-containing material with a surfaceactive agent prior to passing the mixture into the electrostatic field to separate a concentrate rich in the potassium salt.

One of the principal difficulties previously encountered in effecting an electrostatic beneficiation of potash ores has been the presence of water insoluble materials or slimes which efltectively mask the ability of the granules of the feed to assume difierential electrical charges of the required magnitude. The water insoluble materials occurring in most comminuted potash ores owe their origin to the clay-like substances, limestone and anhydrite (CaSO naturally associated with the ore. These materials are usually denominated slimes. Such slimes are removable by scrubbing procedures known to the prior art; however, such procedures are generally undesirable with water soluble materials. Moreover, if potash ore is scrubbed with water or brine to remove slimes, practical economic considerations dictate that the wet ore be beneficiated by flotation rather than subjected to the expensive drying procedures requisite to presenting dry surfaces for dilierential charging in an electrostatic process.

Slime-containing potash minerals may be beneficiated in an electrostatic process and a high total recovery of K 0 may be effected when the mineral is treated with a reagent prior to passing the mineral through the electrostatic field. As the amount of relatively water insoluble constituents, which includes limestone, anhydrite and clays, increases, however, it generally becomes more difficult to produce concentrates of commercially attractive K content at commercially attractive recoveries. ash ores containing more than about by weight of water insolubles are particularly difiicult to upgrade in a process using only an electrostatic separation step. The process of the present invention is eminently suitable for beneficiating such ores.

Accordingly, it is an object of the present invention to provide a commercially attractive method for beneficiating potash minerals.

It is another object of the present invention to provide a combination process for beneficiating potash minerals wherein concentrates of commercial grade may be obtained at a high percentage recovery of K 0.

A further object of the present invention is to provide a process utilizing a combination of electrostatic separation and magnetic separation steps for beneficiating sylvinite ores contaminated with water insoluble constituents.

Generally described, the present invention is a method of beneficiating potassium salt-containing materials contaminated with water insoluble gangue materials which comprises heating a mixture containing discrete granules of potassium salt and discrete granules of gangue material having a particle size of less than about 4 mesh to a temperature of at least about 150 F. and below the fusion point of the ore, differentially charging the heated mixture, passing the differentially charged mixture through an electrostatic field at a temperature not greater than about 500 F. to produce an intermediate potassium salt concentrate containing water insoluble gangue constituents, and subjecting the intermediate potassium salt concentrate to a dry magnetic separation operation to produce a potassium salt concentrate having a higher K 0 content and a lower water insoluble gangue content than said intermediate potassium salt concentrate.

The method of the invention may be practiced, for example, with sylvite-containing ores comminuted to liberation or with particulate sylvite-containing mixtures obtained by evaporation of sylvite-containing brines. The method of the invention is especially effective with materials containing more than 5% by weight of water insoluble constituents and operates to substantially reduce the amount of the water insoluble constituents in the potash concentrate. Potash-containing materials which may be beneficiated by this method include the natural ores such as sylvinite consisting of a mixture of sylvite and halite with small amounts of other minerals; sylvinite ore containing carnallite; mixed ore consisting of magnesium sulfate-potassium sulfate complex, sylvite and halite; langbeinite, consisting of a magnesium sulfate-potassium sulfate complex, and sylvite, and the like; as well as other potash ores which may contain varying amounts of one or more minerals such as anhydrite, kainite, leonite, magnesium sulfate, polyhalite, syngenite, magnesite and limestone, etc., in addition to sylvite; natural salt mixtures and salt mixtures crystallized from naturally occurring brines as well as artificially created brine solutions. As hereinbefore set forth, the process of this invention is particularly effective when the potash-contain ing material contains more than about 5% by weight of slimes.

Regardless of the source of the ore, it is necessary that the sylvite values be liberated from the gangue components of the mixture and be of a mesh size amenable to electrostatic separation in an electrostatic field of practical strength. Accordingly, the materials to be treated are, where necessary, reduced to a particle size of less than about 4 mesh. The lower limit of particle size desirably will be at about 200 mesh, since -200 mesh material creates a serious dust problem and in time builds up a dust layer on the equipment, including the electrodes. The lower limit is more preferably 150 mesh. Further,

'it has been found that the different types of separators available vary in their ability to tolerate fines. For example, it is usually undesirable to employ particles Pot- 4- smaller than -150 mesh with roll-type separators, while the so-called free-fall type separator will effectively separate the smaller particle sizes.

In all electrostatic separations, it is necessary for satisfactory results that the surfaces of the particles be sub stantially dry, thus removing the complicating effects of moisture in the charging and separation step-s. Additionally, it has been found that the ability of some mineral substances to assume and retain differential charges is materially affected, inter alia, by temperature. In the process of the present invention, separations are materially improved by conditioning the comminuted material at a temperature above that necessary merely to obtain dryness. Temperatures above F. and preferably of from about 150 F. to 350 F. are employed although higher temperatures below that at which the particular ore or mixture undergoes incipient vitrification may be employed, i.e., temperatures of 900 F. or above. If desired, the heat-conditioned material may be cooled or allowed to cool before differential charging. However, cooling is not necessary and may not be desirable with some potash materials.

The electrostatic separation step of the process may be effected with an unreagentized material; however, better separations have been effected with reagentized material. When the material is treated with a reagent, preferably a surface-active agent, it may be added to the comminuted mixture to be separated either before or after the heat conditioning step. If added prior to heating, the conditioning temperature employed must be below the decomposition temperature of the reagent. In any event, the reagent, when used, must be added to the mixture to be separated while the mixture is in a substantially dry condition. Moreover, it is desirable in applying the reagent to the dry material to maintain dry reagentizing conditions, i.e., maintaining the particulate material in an unagglomerated condition, as by agitation, while bringing the reagent into contact with the particulate material under conditions whereby substantially no potassium chloride is dissolved and the treated surfaces of the particles rapidly become dry and non-tacky.

The particulate mixture may be reagentized with the agent in any suitable manner. If the reagent is normally liquid, is molten, or is in solution or suspension, it may be poured or sprayed over the particles either while the particles are static or are under agitation. Similarly, the particulate material may be suitably treated with vaporized reagent. Solid reagents may be poured or sifted on the particles. Temperature and/or agitation then may be employed to produce the desired dry, non-tacky surfaces.

Reagents which may be employed in the process of the invention may be selected from a wide variety of materials known to the art. The preferred reagents are surface active agents and preferably are the carboxylic acids and especially saturated and unsaturated fatty acids. Operable acids include without limitation formic, acetic, butyric, propionic, oleic, stearic, lauric, valeric, palmitic, capric, caproic, caprilic, and heptylic acids; naphthenic acids such as hexahydrobenzoic, and diand tetrahydronaphthonic acids; natural resin acids such as abietic, dihydroabietic, pimaric acids; mixtures of resin and fatty acids such as those found in soap skimmings, tall oil and Turkey red oil; sulfonated and sulfated fatty acids; vegetable oil and coconut oil acids, and the like. Carboxylic acid esters such as ethyl hexyl acetate and fatty acid soaps such as the alkali metal soaps of stearic, lauric, oleic, and palmitic acids have been found effective. Sulfonates such as the petroleum sulfonates, sodium keryl benzene sulfonate, sodium polypropylene benzene sulfonate, sodium lauryl sulfonate, and the like, may be employed as surface-active agents as may the long-chain aliphatic amines, such as octadecyl amine, hexadecyl amine, cetyl amine, and the tallow oil, coconut oil, and soya oil amines. Carboxyl amine salts such as rosin amine acetate advantageously also may be employed. Sulfonated alcohols are also effective surface active agents.

The operable reagents heretofore employed in pretreatment of materials prior to electrostatic separation ostensibly have coated selectively certain components of the mixture and not others, thus either altering the conductivity of the coated particle, or its ability to assume a particular charge during contact electrification. When particulate potash ore is treated with surface-active agents, microphotographs of the reagentized feed material surprisingly establish that the surface-active agent preferentially is directed to the slimes adhering to the surfaces of both the sylvite and gangue particles rather than to the particles of sylvite or to the particles of gangue. Accordingly, while greater amounts of reagent may be employed, it has been found that optimum separations are obtained when sufficient reagent is employed to coat only the slimes and not the remainder of the potassium salt and gangue particles. Generally, the amount of reagent employed will be within the range of from about 0.01 to about 10.0 pounds of surface-active agent per ton of the particulate mixture to be treated and separated. With potash ores from the Carlsbad, New Mexico area, from about 0.1 to about 5.0 pounds per ton of particulate mixture is preferably employed. As indicated, the normally solid reagents may be applied in solution or suspension. Since the reagents are employed in small proportions, it frequently is desirable to use an extender such as fuel oil, kerosene, and the like.

In accordance with the present invention, the particles, which may be unreagentized but which are preferably reagentized, are induced to assume differential charges by the mechanism of contact electrification. Contact electrification results from the movement of matter in response to such stimuli as dilferences in escape rate of positive or negative charges, or transfer of electrons or ions across an interface due to differences in energy levels and the like. It has been determined that real crystals never attain the static perfection of an ideal crystal lattice and that a real crystal may have distorted surfaces, displaced ions or atoms, interstitial sites and surface sites, and charge displacement due to separated anion-cation pairs of abnormal ionized atoms and trapped electrons. It is postulated that these traps are capable of acting as donors and acceptors of electrons and frequently it is these traps that are probably the controlling influences in contact electrification of minerals.

Charging by contact electrification normally is obtained by on of two mechanisms, viz., contact with a metal or grounded metal surface or by particle-to-particle contact. When nonconductive particles such as the particles in a liberated potash ore contact a metal or grounded metal plate, the particles normally are charged negatively, but at different magnitudes of charge. When the difference in magnitude is great enough, effective separations are possible. When charging is effected by particle-to-particle contact under conditions present in the method of this invention, the particles of potassium salt and gangue material are charged to opposite polarity and separation is more readily effected. While a relatively small amount of the charging obtained in the process of the invention results from particle-to-metal equipment contact, most of the charging is effected by the more desirable particle-toparticle contacteither as a result of intentional agitation or agitation incident to handling of the feed material during and after the heating and reagentizing steps. The sign of the surface charge to be expected in particle-to-particle contact electrification depends on the probability of the particle making contact with surface A, B, C, etc., and the relation of the surface energies that control the sign of contact electrification of the particles against A, B, C, etc.

It has been discovered that greatly improved differential charging of the particles is accomplished by essentially particle-to-particle contact while the dry comminuted material is maintained at a temperature of at least F. Ideally, the particles would not contact a metal or grounded metal surface during the charging operation, since as previously indicated, contact with grounded metal surfaces usually causes all particles to accept a negative charge. On the other hand, where the charging of the particles is accomplished essentially by particle-to-particle contact while at a temperature of at least 100 F., the surface charge found on the mineral species in the ore is equal and opposite in sign. Accordingly, the charged particles move in opposite directions in an electrostatic field. Thus, in the process of the invention, it becomes possible effectively to separate nonconductive particles.

The desired particle-to-particle charging may be effected in numerous ways, such as by tumbling the particles in a revolving drum or down an elongated chute in such quantity that contact between the particles and chute is at a minimum. Pan pouring also effects differential charging. Alternatively, the comminuted mineral, while maintained at the proper temperature, may be delivered from the drying apparatus to the electrostatic separator by means of a vibrating trough. At high throughput, the great preponderance of charging is engendered by particleto-particle contact rather than by contact of the particles with the apparatus. Suitable charging also may be obtained by air agitation of the hot, comminuted mineral.

Following he preliminary heating, reagentizing, when employed, and differential charging procedures, the particulate mixture then is passed into a suitable electrostatic field -for separtion. At the time of entry into the electrostatic field, the treated material should be at a temperature of at least about 100 F. and preferably at a temperature of F.350 F., although a higher temperature may be employed as previously indicated. Because of the nature of the treatment and charging of the material, the potassium salt and gangue materials are strongly charged to opposite polarity with the result that a good separation often may be achieved in a single pass through an electrostatic field.

As long as the process limitations hereinbefore delineated are observed, the type of separation apparatus employed is not critical, the only limiting factor in terms of apparatus being that the charges on the differentially charged particles be substantially unaltered during de' livery to and passage through the electrostatic field. Accordingly, apparatus with which a material amount of charging by inductive conduction is obtained is not desirably employed. The so-called free-fall type of separator is preferred, inter alia, (a) because the usually employed elongated, vertically disposed electrodes provide longer residence times in the field, (b) because finer particles may be employed than with roll-type equipment, and (0) because the apparatus is less expensive and more easily serviced. However, excellent separations may be achieved with roll-type aparatus wherein the conveyor roll is employed merely as a means of delivering the differentially charged particles to the electrostatic field and substantial charging by inductive conduction is avoided. Suitable free-fall type apparatus is disclosed in US. Patent 2,782,923 to Charles C. Cook et a1. Suitable roll-type apparatus is disclosed in Taggart, Handbook of Mineral Dressing, 1956, chapter 13, such roll-type apparatus being operated to prevent substantial charging by in: ductive conduction.

The strength of the electrostatic field which will effectively alter the normal trajectory of .ore particles depends on the mass of the particle and the total surface charge on the particle. The potential gradient desirably will vary from about 1,000 volts to about 5,000 volts per inch of distance between electrodes in separating material of relatively fine particle size, and from about 3,000 volts to about 15,000 volts per inch for beneficiating coarser particles. In all such discussion of field strength, it must be borne in mind that corona discharges which ionize air are to be avoided. With free-fall apparatus, it

7 generally is preferred to operate with-a total impressed difierence of potential in the range of about 30,000 volts to about 250,000 volts, while with a roll-type separator, a range of about 10,000 volts to about 75,000 volts is preferred. This voltage difference should be maintained by means of a direct current potential source substantially free of ripple. A steady supply of direct current may be obtained with inexpensive filtering apparatus by the use of such equipment as a rectified radio frequency power supply.

Where ore particles are subjected to a series of separations, the feed to subsequent stages often will exhibit progressively reduced response to the electrostatic fields. This reduced response often may be due to loss or leakage of charges from the granular particles or coating of the charged granular particles with fines. Such weakresponding concentrates may be restored or reactivated by passage through an impactor to create new surfaces and again recharging by frictional or other methods that give rise to differential electrification, which recharging may include a reheating in accordance with the treatment hereinabove described. Where a plurality of separation stages is employed, it is also within the scope of the invention to reagentize the granular ore particles between stages.

When a satisfactory beneficiation is not accompilshed in a single stage of electrostatic separation, the usual procedure is to separate a concentrate in a first or so-called rougher stage and to upgrade the concentrate by treatment in two or more so-called cleaner electrostatic separation stages. While the breadth of the range of temperature at the time of passage through the electrostatic field appears adequate to allow for cooling during passage through a plurality of stages it frequently happens that this is not the case. One of the primary reasons for this failure is that in order to reduce the number of separa tion stages, it is desirable to make the first or rougher separation at or near the temperature of about 175 F. to about 300 F., depending on the character of the ore. Concentrate from the rougher separation thus will cool more or less rapidly depending upon the difference in temperature between 200 F. and the atmospheric temperature. After passage through one or more concentrate upgrading stages, it is found that sometimes the potash material has cooled below a temperature at which a measurable degree of upgrading will occur. When the potash ore has become too cool, or picked up too much surface moisture, it sometimes happens that neither the concentrate nor the tail product will respond to further passes through electrostatic fields of the same, lower, or higher potential gradient.

Cooling conditions at times may be such that with some ores requiring a plurality of passes, between about 50% K and about 55% K 0 products can be secured in three consecutive quick passes through electrostatic fields without reheating the solids. On the other hand, cooling of solids as during winter season-s when atmospheric tem-. peratures range, for example, between about 20 F. and about 45 F., may be so fast that precautions must be taken in the handling of a rougher concentrate to obtain satisfactory separation in a first cleaner stage without reheating between the rougher and first cleaner operation. When conditions prevail such that substantial cooling of the ore particles takes place during the operation, reheating is found to be beneficial.

In general, it has been found that where additional passes through an electrostatic field are desirable, a secondary heat treatment whereby the temperature of the solids is maintained at, or is raised to or above 200 F. between separation stages following the first or rougher separation, not only produces concentrates of higher K 0 content, but also reduces the number of separtion stages to obtain concentrates of relatively high K 0 content. Optimum conditions of course exist for various ores and 8 for the various types of electrostatic separators and readily may be determined.

When the material to be separated passes through a series of electrostatic fields, the preferred mode of operation provides for the collection of three fractions from each electrostatic field. How these fractions are further treated depends upon whether the emphasis is on a recovery of a relatively pure tail, a relatively pure concentrate, or both. For example, if emphasis is on the concentrate fraction, the operation of the first or rougher separation stage may be such that a throwaway tail is taken in this very first step. Under such circumstances, the middling fraction is treated in one or more scavenger sections, in which event the tail product from the scavenger section is likewise a throwaway material, and the desired component concentrates of the scavenger section are recycled to a point Where the composition of the material corresponds roughly to the composition of the feed material to a separation unit. In an alternative mode of operation, the rougher concentrate and rougher tail are not final products, and accordingly are subjected to one or more stages of separation to segregate, for example, sylvite from halite. In most instances a middling fraction is recycled either to the feed unit in which it is prepared, or to a point where the composition of the middling corresponds roughly to the composition of the feed material to a separation unit. It will be apparent that many variations may be made in the manipulative steps of the process where it becomes desirable or necessary to subject to a particular feed to a plurality of stages of electrostatic separation.

As liereinbefore set forth, when the potash material to be beneficiated contains more than about 5% weight of water insoluble materials or slimes, concentrates of a predetermined specified K 0 content are not readily obtainable in an electrostatic process at reasonably satisfactory recoveries. It has now been determined that the electrostatic concentrates contain substantial and significant amounts of the water insoluble materials in the original feed. In accordance with the present invention, these electrostatic contrates, containing substantial amounts of water insoluble materials, are upgraded in a magnetic separation operation.

The water insoluble materials or slimes, which includes clays, anhydn'te and limestone, are not ordinarily considered as being amenable to separation from potash ores or concentrates by magnetic methods. The applicant, however, has discovered that the electrostatic concentrate may be substantially upgraded in K 0 content by subjecting the concentrate to a magnetic separation operation whereby substantial amounts of the slimes are removed. Further, it has been found that when the potash ore is a sylvinite type ore, the magnetic separation step not only removes a substantial amount of the slimes, but also, surprisingly, separates a substantial amount of the sodium values from the potassium values.

A potash electrostatic concentrate containing a substantial amount of water insoluble constituents is, in accordance with this invention, subjected to a magnetic separation wherein the concentrate is separated into a magnetic fraction and a non-magnetic fraction. The magnetic separation may be of either the low intensity or high intensity type; however, it preferably is of the high intensity type since much more efiicient separations are achieved with the latter. A high intensity magnetic separator, such as an induction roll type, having a flux density of at least about 25,000 maxwells per square inch and preferably between about 25,000 and about 250,000 maxwells per square inch is used to eifect the separation. The magnetic fraction, which is attracted to and retained by the magnetic separator, contains a large portion of the water insoluble or slime impurities originally present in the feed to the magnetic separator. The magnetic fraction also contains a substantial amount of sodium values when the potash ore feed is of the type containing distinct granules of sodium salt. The nonattracted or non-magnetic fraction which is separately removed from the magnetic separator is substantially enn'ched with respect to K content and the water-insoluble content and Na O content are substantially reduced.

Preferably, the non magnetic fraction is passed through the high intensity magnetic field one or more times. If more than one passage through the magnetic field is made, the intensity of the magnetic field may be held constant for all passes, or separations may be made with progressively higher or lower intensity fields on each pass. In addition, the separations may be made under conditions in which the intensity of the magnetic field is varied from pass to pass. The nature of the potash ore will determine the method of operation that will give an optimum separation.

Having generally described the method of the invention, the following example is given to illustrate specific embodiments thereof.

EXAMPLE A potash ore, of the sylvinite type, had the following approximate mineral composition:

E 0 insolubles, including limestone, anhydrite and clays 9 The ore was crushed and screened to produce a fraction containing particles in the range of 20 mesh to about 150 mesh (Tyler series). The comminuted ore was sprayed with 7 pounds per ton of tall oil per ton of ore. The wall oil used was supplied by the Arizona Chemical Company under the tradename Acintol 1112. The reagentized ore was heated to 500 F. and then tumbled until the ore reached a temperature of about 450 F. The ore was then cooled to about 300 F. by pan pouring. The hot, differentially charged material was then dropped as freely falling bodies through a free-fall type electrostatic separator. The temperature of the ore during the drop was approximately 200 F. The field was maintained between the spaced vertical electrodes of the separator at a gradient of approximately 8,500 volts per inch.

The results of the single pass separation were as follows:

Table 1 Percent K20 Percent Percent K20 Recovery N 2120 Water Insolubles Feed 19.98 100. 00 33. 7 8. 61 Tailing 1. 51 4. 9 50. 3 11.55 Rougher Concentrate 54. 54 95.1 4. 68 2. 79

Table 2 Percent K20 Percent Percent K20 Recovery N azO Water Insolubles Cleaner Concentrate 56. 61 92. 9 3. 8 2. 31 Cleaner Tailing 39. 90 7. 2 14. 6 7. 12

The cleaner concentrate was then subjected to three passes through the high intensity magnetic field of a high intensity induction roll magnetic separator, Carpco standl0 ard laboratory model M-l2, set at 2.0 amp. The field created by the magnetic separator was about 25,000 gauss (161,300 maxwells per square inch).

The results of the high intensity magnetic separation were as follows:

The non-magnetic fraction analyzed 57.9% K 0 and the recovery of K 0 values was 84.9% of the K 0 values in the feed to the electrostatic rougher pass.

This test illustrates that the water insoluble content was reduced from 2.3 to 1.3 in the magnetic separation step. The K O/Na O ratio in the non-magnetic fraction was also much higher than in the magnetic fraction. The magnetic separation, therefore, also upgraded the K 0 content by selectively removing some of the Na O values.

The above example illustrates that potassium salt-containing ores efiectively may be benefioiated by a combination of electrostatic separation and magnetic separation steps when processed in accordance with the present invention.

The description of the invention utilized specific reference to certain process details; however, it is to be understood that such details are illustrative only and not by way of limitation. Other modifications and equivalents of the invention will be apparent to those skilled in the art from the foregoing description.

Iclaim:

l. A method of beneficiating sylvinite ore contaminated with slimes which comprises heating a slime-contaminated mixture containing discrete granules of sylvite and discrete granules of halite having a particle size of less than about 4 mesh to a temperature of at least about F. and below the fusion point of the ore, inducing the mixture to accept differential charges, passing the differentially charged mixture through an electrostatic field at a temperature not greater than about 500 F. to produce an intermediate sylvite concentrate containing halite and slimes, and subjecting the intermediate sylvite concentrate to a dry magnetic separation to produce a sylvite concentrate having a higher K 0 content and a lower halite content and a lower slime content than said intermediate sylvite concentrate.

2. The method according to claim 1 in which the sylvinite ore contains more than about 5% by weight of slimes.

3. A method according to claim 1 in which the granules are 4 +200 mesh.

4. A method according to claim 1 in which the mixture is heated at a temperature between about 100 F. and about 900 F.

5. A method according to claim 1 in which the particles are differentially charged while at a temperature of at least about F.

6. A method according to claim 1 in which the particles are differentially charged by essentially particle-toparticle-contact.

7. A method according to claim 1 in which the differentially charged particles are dropped as freely falling bodies through an electrostatic field created by spaced, oppositely charged electrodes.

8. A method according to claim 1 in which the differentially charged particles are conveyed into an electrostatic field for separation on a roll maintained at ground potential.

9. A method according to claim 1 in which the mixture is treated with a surface active agent prior to differential charging.

10. A method according to claim 1 in which the dry magnetic separation is of the high intensity type.

11. A method according to claim 1 in which the intermediate potassium salt concentrate is passed through a high intensity type magnetic roll separator.

12. A method according to claim 1 in which the heated ore is treated with a surface active agent While substantially dry and While at a temperature of at least 100 F. prior to inducing the ore to assume differential charges.

13. A method of beneficiating sylvinite ore contaminated with at least 5% of slimes which compreses comminuting the ore to a particle size at which the sylvite values are substantially completely liberated from the halite values and the particle size of the comminuted ore is less than about 4 mesh, heating a -20 +150 mesh fraction of the comminuted ore at a temperature of at least 100 F., treating the heated fraction While substantially dry and while at a temperature of at least 100 F. With a surface active agent, inducing the thus-treated fraction While at a temperature of at least 100 F. to assume differential charges, passing the heated, treated, and diiferentially charged fraction While at a temperature of at least 100 F. into an electrostatic field Without substantial alteration of thecharge on the particles to separate an intermediate concentrate rich in sylvite and containing a substantial amount of halite values and slimes, and subjecting said intermediate concentrate to a dry high intensity magnetic separation to produce a potassium chlo ride concentrate having a higher K 0 content, a lower halite content, and a lower slimes content than said intermediate concentrate.

14. A method according to claim 13 in which the surface active agent is composed of at least one carboxylic acid.

15. A method according to claim 13 in Which the particles are differentially charged by essentially particle-toparticle contact.

16. A method according to claim 13 in which the dry high intensity magnetic separation is effected on a roll separator.

References Cited in the file of this patent UNITED STATES PATENTS Weis Sept. 28, 1937 Lawver Sept. 11, 1956 Lawver Sept. 10, 1957 OTHER REFERENCES Industrial Engineering and Chemistry, volume 32, Number 5, May 1940, pages 600-604.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,052,349 September 4 1962 Robert E, Snow It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 26, before "problems" insert process -g line 71, after "effort" insert to column 5 line 1, for "Sulfonated" read Sulfated column 6, line 27 for "he" read the column 7, line 26, for "accompilshed" read accomplished column 8, line 30, strike out "to" a second occurrence; line 41, for "contrates" read concentrates column 9, line 32, for "wall" read tall Signed and sealed this 28th day of May 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. A METHOD OF BENEFICIATING SYLVINITE ORE CONTAMINATION WITH SLIMES WHICH COMPRISES HEATING A SLIME-CONTAMINATED MIXTURE CONTAINING DISCRETE GRANULES OF SYLVITE AND DISCRETE GRANULES OF HALITE HAVING A PARTICLE SIZE OF LESS THAN ABOUT 4 MESH TO A TEMPERATURE OF AT LEAST ABOUT 100*F. AND BELOW THE FUSION POINT OF THEORE, INDUCING THE MIXTURE TO ACCEPT DIFFERENTIAL CHARGES, PASSING THE DIFFERENTIALLY CHARGED MIXTURE THROUGH AN ELECTROSTATIC FIELD AT A TEMPERATURE NOT GREATER THAN ABOUT 500*F. TO PRODUCE AN INTERMEDIATE SYLVITE CONCENTRATION CONTAINING HALITE AND SLIMES, AND SUBJECTING THE INTERMEDIATE SYLVITE CONCENTRATE TO A DRY MAGNETIC SEPARATION TO PRODUCE A SYLVITE CONCENTRATE HAVING A HIGHER K2O CONTENT AND A LOWER HALITE CONTENT AND A LOWER SLIME CONTENT THAN SAID INTERMEDIATE SYLVITE CONCENTRATE. 